Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 230626
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
826 PM HST Fri Sep 22 2017

.SYNOPSIS...
Trade winds will gradually trend down over the weekend as a ridge
of high pressure to the north weakens and a weak surface trough
slowly approaches from the east. Mainly windward clouds with
light passing showers will prevail into early next week, with a
possible boost in shower activity around the middle of next week
as the surface trough moves through the islands.

&&

.DISCUSSION...
Currently at the surface, a 1027 mb high is centered around 1725
miles north-northeast of Honolulu, and is driving moderate trade
winds across the island chain this evening. Meanwhile, a weak
surface trough is located around 550 miles northeast of Hilo.
Infrared satellite imagery shows clear to partly cloudy skies in
place across the State, with some thin cirrus also moving over the
Big Island. Radar imagery shows scattered light showers moving
into windward areas, with a few lingering showers also over
leeward sections of the Big Island. Elsewhere predominantly rain
free conditions prevail. Main short term concerns revolve around
the diminishing trades and rain chances over the next couple of
days.

Tonight through Tuesday,
High pressure will weaken and shift eastward as the weak surface
trough northeast of the state shifts slowly westward toward the
island chain. This will result in a gradual easing of the trade
winds over the weekend, with light to locally moderate trades
expected for the first half of next week. Showers will continue to
favor windward and mauka areas through the period, although some
leeward shower development will be possible each day due to the
weakened trades. Overall, fairly dry conditions are expected
through the period given precipitable waters values in the 1.0 to
1.3 inch range, well below climatological norms for this time of
year.

Tuesday night through next Thursday,
The surface trough will shift westward across the island chain
during the middle of next week, and this should bring an increase
in shower activity, as well as increasing the trade wind flow
back to moderate levels. Showers will continue to favor windward
and mauka areas through the period.

&&

.AVIATION...
Except for the chance of brief MVFR conditions in passing showers
over windward and mauka sections across the island chain, and
TEMPO lower ceilings over leeward sections of the Big Island
tonight; VFR will predominate through Saturday.

AIRMET Tango remains in effect for low level turbulence over and
downwind of the mountains on all islands. This AIRMET will likely
be cancelled by midnight as the trade winds trend down.

&&

.MARINE...
Winds have decreased below Small Craft Advisory (SCA) threshold
this evening, and the earlier SCA for waters around Maui and the
Big Island has been cancelled.

Surf along south facing shores will remain small through early next
week, with mainly background southeast and southwest swell energy
expected. The next potential long-period pulse out of the
southwest from the Tasman Sea is expected by Sunday and could
lead to a slight increase in surf. For the extended forecast,
strong to gale-force southwest winds associated with a low in the
Tasman Sea may lead to another small southwest swell Tuesday
through midweek.

A small northwest swell will continue into the weekend before
easing. Another small reinforcement from that direction is
expected to fill in around Sunday night through the middle of next
week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Jelsema
AVIATION...Kinel
MARINE...Powell



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